Hydropneumatic piston/cylinder arrangement

ABSTRACT

The invention relates to a hydropneumatic piston/cylinder arrangement, in particular for use as a spring element and/or shock absorber element, comprising a cylinder (1) and a piston (15) which is axially movable in the cylinder chamber (5) of said cylinder, the cylinder chamber being tilled with hydraulic fluid. The piston (15) is connected to a piston rod (13) which extends outwards in a sealed manner from one end of the cylinder (1), and the base of said piston, which is remote from the piston rod (13), can he operatively connected to a pneumatic spring mechanism (7) in order to convey fluid. Said piston/cylinder arrangement is characterised in that a piston accumulator (7), the accumulator piston (19) of which directly adjoins the hydraulic fluid situated in the cylinder chamber (5), is provided as the spring mechanism.

The invention relates to a hydropneumatic piston/cylinder arrangement, in particular for use as a spring element and/or as a shock absorber element, comprising a cylinder and a piston, which is axially movable in the cylinder chamber of said cylinder, the cylinder chamber being filled with hydraulic fluid, the piston being connected to a sealed piston rod extending outward from one end of the cylinder, and the base of said piston, which faces away from the piston rod, can be brought into fluid-conducting operative connection with a pneumatic spring mechanism.

Such hydropneumatic piston/cylinder arrangements are known; cf. Japanese Patent Publication 2006070950A, for example. Such piston/cylinder arrangements may be used for various applications, for example, in vehicles, in particular in commercial vehicles, for the axle suspension, or in general technology as vibration dampers or shock absorbers or the like. A compact design of the piston/cylinder arrangement is essential for many applications, in particular for mobile use, e.g., as a spring leg, so that known approaches, such as that disclosed in DE 35 12 232 A1, are not suitable for all applications. This document describes a hydropneumatic axle suspension for vehicles, i.e., for mobile use, but preferably for truck-mounted and mobile cranes, i.e., for heavy vehicles, the chassis of which is supported by hydraulic cylinders on their axles, which are suspended on the frame. The hydraulic cylinders here are connected by hydraulic lines and cutoff valves to hydraulic gas or spring mechanisms which are arranged externally outside of the respective hydraulic cylinder and are connected to inlet and outlet lines for the hydraulic fluid by way of filling and drain valves. Due to the external gas or spring mechanisms plus the respective control system, the required installation space is accordingly high, and secondly, the response of the suspension is subject to a hysteresis and also has a time lag because of the long control distances via the aforementioned valves plus the inlet and outlet lines.

The known approach according to Japanese Publication 1006070950A, as cited in the introduction, overcomes these disadvantages by integrating the pneumatic spring mechanism in the cylinder in the form of a bladder mechanism, but this approach is disadvantageous inasmuch as operational reliability is not ensured in long-term operation because the permeability of the material of the diaphragm of the bladder accumulator results in loss of gas from the bladder accumulator via diffusion. The measures described in the Japanese document to prevent gas diffusion by coating the diaphragm with an amorphous carbon layer are complex and do not offer absolute protection against gas diffusion through the membrane.

Based on these problems, the object of the present invention is to make available a hydropneumatic piston/cylinder arrangement that is characterized by a high operational reliability in long-term operation despite the compact design.

According to the invention, this objective is achieved by a hydropneumatic piston/cylinder arrangement having the features of Patent Claim 1 in its totality.

One important special feature of the invention thus consists of the fact that a piston element is provided as the spring element, its accumulator piston being directly adjacent to the hydraulic fluid in the cylinder chamber. When the piston accumulator is integrated into the cylinder, not only does this eliminate the external components that take up installation space, such as those which are necessary in an external spring element, but also the integrated piston accumulator yields a much greater operational reliability in comparison with a bladder accumulator, not only with regard to preventing gas diffusion through a diaphragm material but also with regard to the greater mechanical sturdiness in comparison with an accumulator diaphragm.

In a particularly advantageous manner, the cylinder chamber for the hydraulic fluid and the chamber of the piston accumulator that is delimited on the gas side by the accumulator piston may be formed by a cylinder liner passing seamlessly from one end to the other. Therefore, the entire arrangement forms a compact and uniform component, which is especially suitable for installation in devices with limited available space, for example, in a spring leg.

In especially advantageous exemplary embodiments, an intermediate body is arranged in an axially stationary manner between the accumulator piston and the piston connected to the piston rod, at least one fluid passage enabling the provision of a predetermined flow in said cylinder chamber. The damping and shock absorber characteristics of the arrangement can be optimally adapted as needed through an appropriate design of the fluid passage and the corresponding size of the volume flows that are displaced with the movements of the piston connected to the piston rod through the fluid flow in the intermediate body.

The fluid passage in the intermediate body may be provided in the form of a through-hole, which is dimensioned for the volume flows that are provided accordingly. Alternatively, and preferably in addition to the through-hole, a fluid passage in the form of a throttle check valve may be provided in the intermediate body. This yields the possibility of designing the volume flows created with the piston movements to be different in one stroke direction and in the other stroke direction, so that rapid damping in one stroke direction is induced with a throttled reverse movement accordingly. This also dissipates vibration in the system.

A throttle check valve, having a valve plate in which there is a borehole to form a throttling point, may be provided, especially advantageously, in the case of an installation space which is available to a limited extent in the axial direction inside the intermediate body. A functionally corresponding throttle check valve is known from the document DE 103 37 744 B3 per se.

The intermediate body may be provided in the form of a round plate that can be accommodated to fit in the cylinder and is secured axially in the cylinder by means of at least one spring ring, for example.

For an additional throttle effect, independently of the piston connected to the piston rod in the tension direction and in the compression direction, it is also possible to provide a throttle check valve in the piston, permitting a limited fluid flow from the front side of the piston to the rear side of the piston adjacent to the piston rod, i.e., to a chamber, which is closed on the cylinder end, i.e., to a closed chamber situated at the end of the cylinder, from which the piston rod extends out of the cylinder with a seal.

The invention is explained in detail below on the basis of the drawings, which show:

FIG. 1 a schematic simplified longitudinal section of an exemplary embodiment of the piston/cylinder arrangement according to the invention;

FIG. 2 in a diagram corresponding to FIG. 1, a breakaway partial longitudinal section of only the end area on the fluid side of an exemplary embodiment that has been modified in comparison with FIG. 1;

FIG. 3 a longitudinal section which is enlarged with respect to FIGS. 1 and 2, showing only an intermediate body for use in the exemplary embodiments according to FIG. 1 or FIG. 2 and

FIG. 4 a cross-section through the intermediate body according to sectional line IV- IV in FIG. 3.

In the exemplary embodiments shown in the drawings, the cylinder 1 is in the form of a cylinder liner 3, which extends seamlessly from the cylinder chamber 5, forming the fluid side, to the spring accumulator 7 that is integrated into the cylinder liner 3. On the lower end in FIG. 1 belonging to the spring accumulator 7, the cylinder liner 3 is sealed by a closing plate 9, which is bolted or welded in place. A corresponding filling connection located in the closing plate 9 for filling the spring accumulator 7 with working gas (e.g., N₂) is not shown in the simplified diagram in FIG. 1. On the end having the closure cap 9, a fastening eye 11 is welded or bolted onto the cylinder liner 3. The piston rod 13 of a piston 15, which is movable in the cylinder chamber 5 on the fluid side, passes through the opposite closed upper end of the cylinder liner 3 with a fluid-tight seal by means of sealing elements 17. The spring accumulator 7 is formed on the piston accumulator, having an accumulator piston 19, which is in the form of a shallow pot that is open toward the accumulator 7 and is provided as a movable separation element between the cylinder chamber 5 and the accumulator 7.

In an axial position, which is adapted to the permissible stroke length of the piston 15 connected to the piston rod 19 in operation, an intermediate body 21 in the form of a flat circular plate, which fits the inside wall of the cylinder liner 3 circumferentially and is secured axially thereon, for example, by means of spring rings sitting in grooves (not shown in the drawing), is situated inside the cylinder chamber 5 on the fluid side. Despite the extensive contact of the intermediate body 21 with the cylinder liner 3, the intermediate body 21 does not form a sealing dividing element for the fluid (hydraulic fluid) inside the cylinder chamber 5, but instead is provided with devices that allow fluid to pass through. These devices are designed so that volume flows of the desired extent are displaced through the flow devices with the stroke movements of the working piston 15. In the example in FIG. 1, a through-hole 23 having a diameter adapted to the use conditions is provided for this purpose. In FIG. 1, in addition to the through-hole 23, a throttle check valve 25 is disposed in the intermediate body 21, permitting a more throttled volume flow in one direction of flow than in the other direction of flow. Whereas both measures, namely the through-hole 23 and the throttle check valve 25, are provided in the intermediate body 21 in FIG. 1, the borehole 23 alone or the throttle check valve 25 alone could also form the fluid passage.

FIGS. 3 and 4 illustrate a possible design of the throttle check valve 25 in the form of a type of plate valve. With the chamber available in the axial direction inside the intermediate body 21, such a valve design as the one that is known principially from DE 103 37 744 B3 is especially suitable. As FIGS. 3 and 4 show, a valve plate 27, which is in a valve housing 29 inside the intermediate body 21, is provided as the movable valve body. This valve housing is open at the lower end in FIG. 3, apart from supporting bodies 31 protruding radially inward at the opening edge. On the opposite top side of the intermediate body 21, the valve housing 29 has a valve opening 33, which can be closed by the valve plate 27, which is shown in its closed position in FIG. 3. In the closed position, the fluid passage through the valve bore 33 is blocked, apart from a throttled volume flow, which is possible in the closed position through a throttle bore 35 provided in the central area of the valve plate 27.

The valve plate 27 in the example shown here has an essentially quadratic outline, which describes a smaller area than that corresponding to the cross-section of the valve housing 29, so that when the valve plate 27 moves out of the closed position (downward in FIG. 3) and is no longer in sealing contact with the edge of the valve opening 33, the flow passes around the valve plate 27 at the side, so that in the open position a relatively large flow cross-section is available. When the valve plate 27 is lifted away from the edge of the valve opening 33, the valve plate 27 with the base parts 37, which are bent obliquely outward at the corner areas, is supported on the supporting bodies 31. Other than the base parts 37, which are bent outward after insertion of the valve plate 27 into the valve housing 29, the valve plate 27 has a guide lug protrusion 39 (not shown in FIG. 3 for the sake of simplicity), which can be bent for insertion into the valve housing 29 and can be brought into engagement with a guide groove 41 extending axially in the valve housing 29, forming, together with the lug 39, a twist-proof lock for the valve plate 27.

In the example shown here, the valve plate 27 basically has a quadratic perimeter. It is self-evident that other shapes could also be possible, for example, a triangular shape or the like, on the condition that the outline of the plate is smaller than the opening cross-section of the valve housing 29, so that, in the opened position, enough flow cross-section is available at the edge of the valve plate.

FIG. 2 shows another variant. In this exemplary embodiment, a throttle check valve 45 is also integrated in the piston 15 connected to the piston rod 13, so that an additional means is available, thus permitting an adjustment of the damping characteristics and/or spring characteristics to the use conditions. 

1. A hydropneumatic piston/cylinder arrangement, in particular for use as a spring element and/or shock absorber element, comprising a cylinder (1) and a piston (15), the piston being axially movable in the cylinder chamber (5) of said cylinder, which is filled with hydraulic fluid, said piston being connected to a sealed piston rod (13) extending outward from one end of the cylinder (1), the base of said piston, facing away from the piston rod (13), can be brought into a fluid-carrying operative connection with a pneumatic spring mechanism (7), characterized in that a piston accumulator (7), the accumulator piston (19) of which is directly adjacent to the hydraulic fluid in the cylinder chamber (5), is provided as the spring mechanism.
 2. The piston/cylinder arrangement according to claim 1, characterized in that the cylinder chamber (5) for the hydraulic fluid, and the chamber of the piston accumulator (7) on the gas end delimited by the accumulator piston (19), are formed by a cylinder liner (3) passing seamlessly from one end to the next.
 3. The piston/cylinder arrangement according to claim 1, characterized in that an intermediate body (21) is disposed such that it is axially stationary, in the cylinder chamber (5) between the piston (15) connected to the piston rod (13) and the accumulator piston (19), with at least one fluid passage (23, 25) which permits a predetermined flow being provided therein.
 4. The piston/cylinder arrangement according to claim 1, characterized in that a fluid passage in the form of a through-hole (23) is provided in the intermediate body (21).
 5. The piston/cylinder arrangement according to claim 1, characterized in that a fluid passage in the form of a throttle check valve (25) is provided in the intermediate body (21).
 6. The piston/cylinder arrangement according to claim 1, characterized in that a throttle check valve (25) is provided with a valve plate (27) in which a borehole (35) is present to form a throttling point.
 7. The piston/cylinder arrangement according to claim 1, characterized in that an intermediate body (21) in the form of a round plate that fits and can be accommodated in the cylinder (1) is provided, said plate being secured axially in the cylinder (1) by means of at least one spring ring.
 8. The piston/cylinder arrangement according to claim 1, characterized in that a throttle check valve (45) permits a limited fluid flow from the front side of the piston to the rear side of the piston adjacent to the piston rod (13) in the piston (15), which is connected to the piston rod (13). 